The subject matter of the present invention relates generally to saw chain for chain saws and in particular to saw chain having cutter links with a central pivot on the bottom edge of such cutter link which contacts the saw bar track to tilt the cutter link backward and forward during cutting to reduce vibration.
As saw chain is moved along the track of the saw bar of a chain saw it causes considerable vibration when the cutter links of such chain engage wood during cutting. This vibration is produced at least in part because the cutter links dig into the wood and tend to rear up when they pivot about the rear foot portion of the cutter link on the saw bar which raises the depth gauge portion and causes the cutter link to reduce its cutting edge penetration. When the cutter cuts through the wood to produce a severed wood chip it pivots back down so that its front foot portion contacts the saw bar track with considerable force. The repeated back and forth pivoting of the cutting link results in a hammering action on the saw bar thereby producing vibration which is transmitted to the hands of the chain saw operator. This vibration can cause injury to the hands of the operator of various types including Raynaud's Syndrome, numbness, muscle fatigue, tendonitis and the like. Previous attempts to solve this saw chain vibration problem have not been entirely successful.
As shown in U.S. Pat. No. 4,567,803 of Anderson, issued Feb. 4, 1986, it is known to provide a so-called anti-kick safety saw chain with guard links mounted in front of the cutter links to prevent the depth gauge or other portion of the cutter links from digging into the wood and causing kickback. In order to reduce the vibration of such a safety chain, it has been proposed in U.S. Pat. No. 4,643,065 of MacGavin, issued Feb. 17, 1987, to provide such guard links with a rear foot portion which is cut away to space such rear portion from the saw bar to enable the safety link to pivot without impacting such saw bar and reduce vibration.
An early attempt to reduce vibration of a conventional saw chain without guard links is shown in U.S. Pat. No. 4,122,741 of Engman, et al., issued Oct. 31, 1978. The Engman patent shows a saw chain having a side cutter link with the rear foot portion or heel at the bottom of the cutter link cut away to raise up and space such heel from the saw bar. The side link tie strap on the opposite side of the chain from such cutter is also provided with a raised heel portion spaced from the saw bar. This raised heel causes the cutting link to pivot about a front foot portion which contacts the saw bar track under the front rivet during cutting so that the cutting edge of the cutter link tends to pivot downward, thereby lowering the cutting edge rather than raising it to prevent such cutting edge from further digging into the wood as occurs when such cutter link pivots about a rear foot under the rear rivet. In a second embodiment, this patent provides a cutter link in which both the front foot portion and rear foot portion of such link are cut away and raised up so they are spaced from the saw bar during cutting. This causes the chain to pivot about the rear rivet of the preceding side link tie strap thereby even more effectively preventing the cutting edge of the cutter link from raising during cutting to reduce vibration.
U.S. Pat. No. 4,573,386 of Lindemann, et al., issued Mar. 4, 1986, shows a saw chain in which the rear foot portion of the cutter link is cut away so that such rear foot portion contacts the saw bar only at a tilt point ahead of the rear rivet opening to cause the cutter link to tilt about the tilt point. This reduces the amount of tilt elevation of the cutting edge when such cutter link engages wood thereby reducing tilt displacement of the cutting edge during cutting and partially reducing vibration. However, the front foot portion of the cutting link engages the saw bar at a position ahead of the forward rivet opening so that cutting results in continued tilting of the cutter link up and down about the tilt edge causing the front foot portion of the cutter link to slam repeatedly into contact with the saw bar with a hammering action which still transmits considerable vibration to the saw bar and the chain saw operator's hands.
Other attempts to reduce vibration in saw chain operation include using a center drive cutter link as shown in U.S. Pat. No. 4,898,057 of Hille, issued Feb. 6, 1990. In this chain the side link tie strap connected to the rear rivet of the center cutter link has been shaved away at its front foot portion to space such front foot away from the saw bar. Here again, this reduces tilt displacement of the cutting edge by causing the center cutter link to pivot about its forward rivet rather than its rearward rivet which results in the cutting edge moving downward rather than raising further into the wood when it engages the wood during cutting. However, a center cutter link saw chain is not as desirable in some circumstances as saw chain with side cutter links which employs alternate cutters on opposite sides of the chain with left-handed and right-handed cutter congfiguration for more efficient cutting.
The saw chain of the present invention employs side cutter links of improved design with a central pivot which contacts the saw bar to tilt about such pivot for reduced vibration and efficient cutting.
The cutter link of the present invention has a rear foot portion extending from a central pivot to the rear of the cutter link which is normally spaced from the track of the saw bar. In addition such cutter link has a front foot portion extending from such pivot to the front end of the cutter link which is also normally spaced from said track. This allows the cutter link to pivot or tilt about the central pivot in both a rearward and a forward direction by a significant amount without striking the saw bar with either the front or rear foot portion of the cutter thereby reducing vibration during cutting. In one embodiment of the present invention, the central pivot is provided by a single pivot point located centrally of the forward rivet opening and the rearward rivet opening of the cutter link. In another embodiment the pivot is provided by a pair of central pivot points longitudinally spaced apart and both located between the forward rivet opening and the rearward rivet opening of the cutter link. In addition, the tie strap side link on opposite side of the saw chain from the cutter link is provided with a central pivot located between the forward rivet opening and the rearward rivet opening of such tie strap which contacts the saw bar for tilting about such pivot in a similar manner to the cutter link. The saw chain of the present invention not only reduces vibration but also operates with efficient cutting by employing side cutter links with right-handed and left-handed cutters alternating along the length of such chain. The saw chain may be provided with a guard link portion on the top of the center drive link to protect the front of the depth gauge of the cutter link thereby reducing kickback. Thus, the cutting chain of the present invention operates in a safer manner than cutting chains not employing such guard links.